Assignment # 6
1.Which regulatory mechanisms occur at the DNA-level, which occur at the protein-level?
Answer: The regulatory mechanisms that occur at the DNA-level are ones that A. prevent mRNA from being transcribed B. involve transcription factors or chromatin remodeling factors.
The regulatory mechanisms that occur at a protein level are ones that A. prevent enzymes from doing their jobs B. involve factors that disable or degrade the enzyme C. are usually controlled by feedback inhibition.
2.How do acetylation, methylation, repressors, activators, and siRNA control gene expression? What role do inducers play?
Answer: Histone "acetylation", DNA "methylation" repressors, activators and siRNA control gene expression through the following: acetylation enable the DNA to be "loose" enough to allow transcription machinery repressors bind to regulatory sites blocking attachment of transcrption factors. Activators bind to regulatory sites associated with a gene. siRNA are "short interfering" RNA that are 20-25 Ribonucleotide-long segments of RNA that bind to mRNA blocking it from being translated into a protein. Inducers function by disabling repressor proteins, thus the repressor proteins bind to the DNA strand and prevent the RNA polymerase from attaching to the DNA and synthesizing mRNA. Inducers bind to repressors which causes them to change shape and prevents them from binding to DNA, therefore allowing transcription followed by gene expression.
3.What is an enhancer and how does it help control how much of a particular protein is made?
Answer: An "enhancer" is a regulatory site from a promoter.
4.How do allosteric inhibition and competitive inhibition differ in the ways they accomplish feedback inhibition?
Answer: To accomplish feedback inhibition allosteric inhibition is very specific and is accomplished only by isoleucine, which binds to a site on the enzyme molecule called the "regulatory", or allosteric site. This site is different from the active site of the enzyme, which is the site of the catalytic action of the enzyme on the substrate. The way that competetive inhibition accomplishes feedback inhibition is that the inhibitor binds ONLY to the free enzyme and CANNOT bind when the substrate is bound.
5.What are the three phases of the cell cycle? What occurs at each phase?
Answer: Interphase, Mitosis, Cytokinesis
Interphase: the phase of the cell cycle in which the cell spends the majority of its time performing the majority of the purposes needed which include: the preperation for cell division.
Mitosis: a process in which a eukaryotic cell seperates the chromosomes in its cell nucleus into two identical sets of nuclei.
Cytokinesis: the process in which the cytoplasm of a single eukaryotic cell divides to form two daughter cells. Cytokinesis is usually initiated during the last stages of Mitosis and sometimes Meiosis.
6.What are the four phases of mitosis? What occurs at each phase?
Answer: prophase, metaphase, anaphase, telophase.
Prophase: the stage of mitosis in which the chromatin is condensed into a highly ordered structure called a chromosome were the chromatin becomes visible. It is when the DNA condensesw and the nuclear envelope dissolves, then the mitotic spindle starts to develop from the centrioles.
Metaphase: when the chromatids line up along the center of the cell, then the centromeres attach to fibers of the mitotic spindle.
Anaphase: occurs when the fibers of the mitotic spindle shorten causing the chromatids to pull apart. The chromatids pull apart so that the identical strands of DNA for each chromosome goes to one side of the cell while the other moves towards the opposite side. All of this results in each new cell having a full set of chromosomes.
Telophase: During telophase, the effects of prophase and prometaphase events are reversed and so two daughter nuclei form in the cell. The nuclear envelopes of the daughter cells are formed from the fragments of the nuclear envelope of the parent cell and then the nuclear envelope forms around each pair of chromatids, making the nucleoli reappear.
7.What are cell cycle checkpoints? Why are they important?
Answer: The cell cycle checkpoints are the G1, G2 and Metaphase checkpoint. Checkpoints are important because enzymes block the cell cycle from progressing until certain conditions are met.
8.What is apoptosis? What role does it play in the cell cycle?
Answer: Apoptosis is the process of programmed cell death
9.What is the difference between chromatin and chromosomes?
Answer: Chromatin has a Nuclear pore and Nucleosomes and Chromosomes have a Telomere and Centromere.
10.What is the role of the centromere? (What would happen without it?)
Answer: Centromeres are proteins that attach sister chromatids together. They are usually located in the center of the chromatids. The two sister chromatids together create a chromosome. The chromatids stay together with the centromeres until anaphase, when they separate into the two new daughter cells.
11.What is the difference between a chromatid and a chromosome?
Answer: When the chromosome is duplicated it's called sister chromatids, and so each one of them is called a chromatid. At times sister chromatids will be called as "chromosomes.
12.What events must happen in order for two sister chromatids to separate from one another and move to opposite sides of the cell? (What happens at the centromere? What happens to the centromere? What is the role of the mitotic spindle?)
Answer: During Anaphase sister chromatids are pulled apart and start moving to opposite sides of the cell. In the third stage of anaphase is when the sister chromatids of each replicated chromosome begin to separate. The fibers pull the centromere apart and the chromatids move away from one another towards the opposite end of the cell.
13.What would happen if two sister chromatids moved to the same side of the cell?
Answer: the fibers would not pull apart.
14.What happens to the mitotic spindle after mitosis?
Answer: The mitotic spindle breaks down after mitosis.
15.What are gametes? Where are they made in the body? How are they made?
Answer: A gamete is a reproductive cell having the haploid number of chromosomes, especially when a mature sperm or egg is capable of fusing with a gamete of the opposite sex to produce a fertilized egg. For gametes to form the gametes require cells to undergo a special type of cell division called meiosis, which is really two cell divisions happening one after the other.
16.What are the eight phases of meiosis? What occurs during each phase? How does meiosis differ from mitosis?
Answer: Prophase 1-->Metaphase1--> Anaphase1--> Telophase1/Cytokinesis-->Prophase 2-->Metaphase2--> Anaphase2--> Telophase2/Cytokinesis
17.How do crossing over and random assortment “mix up” genes so that children are genetically different from their parents?
18.Why are insertion and deletion mutations usually more harmful than substitution mutations?
19.How does nondisjunction affect the genes present in an organism? Specifically, why does it cause deformities?
20.What “super powers” must a cell acquire to become cancerous? How does it acquire these powers?
21.Compare and contrast oncogenes and tumor suppressor genes. What are they? How are they similar? How are they different?
22.Why is cancer primarily a disease of old age?
23.How do mutations cause genetic variation? Is this good or bad for the organism?
24.How do genetic diseases caused by point mutations differ from those caused by chromosomal mutations like nondisjunction?
25.What causes spontaneous mutations? What causes induced mutations?
26.How accurate is DNA replication? (That is, how often do point mutations occur?)
27.What type of mutation is shown here? AGTGCCGTCAC TCACGGCCAGTG
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